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Abstract

Background and Objective Rabbitfish Siganus rivulatus is one of the ecologically and commercially important marine fish inhabiting Egyptian northwestern Mediterranean Coastal regions. Studying the reproductive biology of fish species is among the most important life-history parameters that researchers must establish. The present study was carried out to test the theory of variation in the reproductive biology of rabbitfish Siganus genus and determine the exact spawning season of Siganus rivulatus species. Material and Methods Random monthly samples of wild fresh dead fish were collected from Alexandria December, 2016 to November, 2017. Biometric measures total length, weight, gutted weight and ovary weight were carried out. The fish was dissected and ovarian samples were collected and weighed monthly average n 20 throughout the year to identify the macroscopic and microscopic features of different maturity stages, determine gonadosomatic index values and fecundity. Results Monthly analysis of the maturity stages distribution and gonadosomatic index recognized one distinct peak in June, identifying the spawning season late May to mid of July. The morphological appearance and histological examination of the ovaries together with the ultrastructural changes in the oocytes wall showed that this species is an annual synchronous oocyte developer and their release takes place over a short period. Conclusion Siganus rivulatus has a short spawning period extending from late May to mid of July the current study with an annual seasonal variation depending on different environmental factors. This study recommends the determination of the exact timing of the spawning season for this fish species annually as a basic mariculture practice due to its ecological and economical implication.